1. Technical Field
The present invention generally relates to display fields and, particularly to a gate pulse modulation circuit and a sloping modulation method adapted thereto.
2. Description of the Related Art
Nowadays, a driving method of a thin film transistor liquid crystal display (TFT-LCD) device is using a gate pulse signal to drive each pixel transistor for controlling on-off states of each pixel. When a gate pulse signal is inputted to switch on the pixel transistor, a data signal desired to be displayed will be delivered to the pixel through the pixel transistor. If the pixel transistor is switched off, the data signal desired to be displayed would not be delivered to the pixel through the pixel transistor.
In a pixel array of a display panel, each pixel can be considered to be constituted by an equivalent resistor and an equivalent capacitor. In such situation, a front-end inputted waveform and a rear-end waveform on a same scan line associated with each gate pulse signal scanning are different from each other, termed as waveform distortion (reasons for the signal distortion are relevant to high frequency components in the signal are filtered off by the resistor-capacitor low pass filter), Accordingly, it is necessary to modulate e.g., sloping the gate pulse signal, so that the front-end inputted waveform and the rear-end waveform on each scan line are approximately the same, so as to relieve the image flicker phenomenon caused by different feed through voltages on the front-end and the rear-end.
In the prior art, a gate pulse modulation circuit has been proposed to carry out a sloping modulation applied to a gate power supply voltage signal, so as to obtain a sloped voltage signal and output the sloped voltage signal to a gate driver for deciding the waveform of a modulated gate pulse signal. In particular, as illustrated in FIG. 1, an internal circuit diagram of a gate pulse modulation circuit in the prior art is shown. The gate pulse modulation circuit 50 includes a voltage modulation circuit 52 and a diode D0. The voltage modulation circuit 52 is electrically coupled between a gate power supply voltage VGH and a ground voltage AVSS and subjected to the control of a sloping control signal YV1C to alternately switch on internal transistors Mp, Mn, so as to carry out a sloping operation and thereby output a sloped voltage signal VGHM on an output terminal 51 of the gate pulse modulation circuit 50. A positive electrode of the diode D0 is electrically coupled to a power supply voltage AVDD, and a negative electrode of the diode D0 is electrically coupled to a node n1 in the voltage modulation circuit 52. Herein, the gate power supply voltage VGH is provided from a charge pump circuit 100, the sloped voltage signal VGHM is supplied to the gate driver 200 for the use of gate pulse modulation, and the node n1 is arranged at the source of the transistor Mn and electrically coupled to the ground voltage AVSS through a discharge resistor Radj.
Referring to FIG. 2, a measured waveform diagram of a gate pulse signal generated from the gate driver 200 as illustrated in FIG. 1 is shown. The prior art use the conduction characteristics of the diode D0 that being on when forward-biased and off when reverse-biased, to periodically deliver the power supply voltage AVDD to the output terminal 51 of the gate pulse modulation circuit 50, so as to control the lower limit of the sloped voltage signal VGHM (i.e., corresponding to the portion circled by a dashed circle in FIG. 2). However, it is found in FIG. 2 that the lower limit of the sloped voltage signal VGHM is not a constant value, one of reasons may be that the lower limit is influenced by the inherent conduction characteristic of the diode D0, so that the image flicker phenomenon could not be effectively improved. Accordingly, it is necessary to propose an improved gate pulse modulation circuit, a lower limit of a sloped voltage signal outputted therefrom would not be effected by the conduction characteristic of diode in the prior art and can keep unchanged, so that the image flicker phenomenon can be improved.